In automatic transmissions, which are increasingly being used in motor vehicles, sensors are used which transmit more than one information item. One example is the engine-speed sensor, which measures both the rotational speed and the direction of rotation. The measured information items may be transmitted to a control unit via digital signals, e.g., via a bit code, or via analog signals, thus, e.g., using the ratio of signal voltage to sensor supply voltage. In order to achieve a high degree of transmission reliability, PWM (pulse-width-modulation) interfaces are increasingly being used. In the case of these, the ratio of the pulse width, also known as the pulse duration, and the signal period, also known as the period, is evaluated. However, PWM interfaces have the disadvantage that only information items regarding one physical variable can be transmitted. It is not possible to transmit independent variables via PWM interfaces.
A sensor for a transmission control system of, in particular, a motor vehicle is described in German Patent No. DE 10 2004 024 954. The sensor is connectible to a supply voltage VS and to ground GND, the sensor generating a signal voltage Vout. The signal voltage can assume two signals, namely HIGH and LOW, the two signals HIGH and LOW differing from supply voltage VS and from ground GND. The two signals HIGH and LOW take the form of, in particular, pulse-width-modulated signals.